There are a variety of portable electronic devices in common use by many people for a number of different tasks. Not the least of which is the cellular or radio telephone and other mobile communication devices. These devices are all battery powered, and because of their relatively high power consumption they typically employ rechargeable batteries due to the high operating cost that would be incurred with primary batteries.
Rechargeable batteries are typically recharged according to a charge regime, meaning prescribed voltage and/or current levels and limits are applied to the battery, and other factors such as change in voltage, current, temperature, or a combination of these, may be taken into account to determine when the battery is finished charging. For example, nickel-based batteries are often monitored for temperature and voltage changes. Lithium-ion batteries are typically charged using a constant current to constant voltage regime, where the voltage level during the constant voltage phase is carefully controlled.
In charging lithium-ion batteries, it has been found that the voltage level used during the constant voltage phase affects cycle life of the battery. The higher the voltage limit used, the more the cycle life of the battery is reduced. Since manufactures often warranty battery cycle life, the charge voltage limit as carefully selected to balance optimum charge capacity with cycle life of the battery. However, at the expense of cycle life, a lithium ion battery may be recharged to a capacity higher than its nominal capacity by setting the charge limit voltage higher than a standard or normal level. Since battery cycle life is warranted, though, chargers and charge controllers for lithium-ion batteries are designed with a fixed charge voltage limit. In some situations, however, users may wish to achieve higher capacity at the sake of cycle life, and possibly altering or voiding a battery warranty. Therefore there is a need for battery charger that allows selectivity in recharging a lithium-ion battery with regard to charge voltage limit.